losetup /dev/loop0
loop: can't get info on device /dev/loop0: No such device or address

losetup /dev/loop8
loop: can't open device /dev/loop8: No such device or address

Now let me create two files and setup the two loop devices. As in the link, loop0 succeeds while loop8 fails.Two device comparison

Why is this the case?

PS. On an extra note, if I restart the computer, it always has loop0~loop7 even if you create or remove any loop devices. Furthermore, as shown in the first link, the time they are edited are all at bootup. Finally, even if you setup /dev/loop0 with a file, after computer reboot, despite /dev/loop0 existing, /dev/loop0 is no longer set up. I have no idea why these are happening.